I’m looking to have a push button turn on a bright LED for about 5 minutes and then shut down with very low leakage current (<10uA). I’ve played with a 555 timer circuit, but the leakage is too high (>200uA) as this will be a very low power/battery product.
What is the best way to accomplish this? Thanks in advance!
Hello @dantopolsky,
Sorry for the long delay in getting back to you. This took some digging around to look at possible options. My first thought was to go with a manual time delay relay, however limited voltage options and price make these generally a non-option. Another option maybe a latching relay that your 555 timer unlatches. you would still have the larger current, however only during use.
One of my engineers suggested looking at the following parts. TPL5110DDCT or TPL5111DDCT There would be some additional circuitry, however you are looking at 35nA.
Some additional parts you could look at.
MC14541BDG
MC14536BDWR2G
Thank you
-Robert
Thanks Robert!
Those solutions might work, but the unit prices are quite high. For comparison sake, I found a Chinese circuit that does exactly what I want called the C005 (see links below) for <$0.13/unit. Are you familiar with this? I believe that it’s probably a similar, but simpler circuit to what you proposed all integrated into one Silicon chip with external R for setting the time delay.
https://www.yoycart.com/Product/25455272178/
http://www.talkingelectronics.com/projects/50%20-%20555%20Circuits/50%20-%20555%20Circuits.html (the circuit is demonstrated on this Hobbyist’s page)
Let me know what you think. Thanks again for your help!
Hello @dantopolsky,
I am not aware of the chip they are using so it is hard to give an opinion. It is even harder when the manufacturer (who ever that may be) does not give a complete data sheet with electrical specs. Hard to say if it meets the specs you are asking for.
The board appears to be similar to the 1528-1917-ND board from Adafruit Of course they do not appear to be using the done portion. For your application it would not be needed. 1528-2379-ND would be another board you could look at.
While it is true the price for the chinese chip itself is slightly less (depending on volume) I think you will find the parts tend to be of higher quality when they come from a manufacturer you can trust and a Distributor that will stand behind the parts.
I could also recommend a 5555 programmable timer such as 1727-5961-1-ND.
It does require some external components to operate properly, but it does allow for timing selection and is power efficient while in idle ~100uA, it also has a wide operating voltage range, which is beneficial for battery operations.
The down side may be the maximum output current that an output pin can provide is ~20mA, so you would need a switching device if the LED draws more than that.
Just one more option,
Thanks,
Reid L.
Thanks Robert!
Yes, using that cheap part definitely would make me nervous. That Adafruit board looks like it will do the trick to try out the TPL5110. I will try it out. Can you tell me which MOSFET is best suited for the TPL5110 to drive <30mA of current into a LED? I should be able to use the
RZM001P02T2L right? Any concerns there?
Thanks Reid!
The 5555 looks like it would work, but it’s probably overkill for my project. I will keep it in mind.
If you are looking at just the chip that should work. If you are looking at trying the board for quick testing you will not need a fet as they have the DMG3415U-7 mounted right on the board. There is also a mounted LED that will show functionality.
Thanks Robert!
Also, do you know what LED is mounted to the board?
Also, can you recommend an SMT LED kit to get an idea of what LED options are out there?
I am sorry I was not able to identify which LED they are using outside of the fact that it is a green led.
We really don’t have a good SMD LED kit for showing different options. Best I would suggest it to look at this list of SMD LEDs and decide what your requirements will be for voltage, color, mcd and size and go from there. I know the list is long but you can really use a lot of different options.
Let me know if you have any more questions I can help with.
-Robert
https://www.digikey.com/schemeit/project/pushbutton-monostable-B1K6I08403PG/
See above schematic. This is another method using only 3 small parts and next to zero leakage current is to run the LED through a Mosfet -this can be using the same or different power supply as long as grounds are tied. Have a capacitor in parallel with a resistor across the gate and ground. The pushbutton would momentarily provide voltage to the gate, charging the capacitor which will keep the mosfet on after the button is released. The resistor in parallel with the capacitor will be responsible for discharging the capacitor (also functions as a pull-down resistor), and depending on the resistance and capacity selected, will determine how long the LED will stay on.
I would recommend experimenting with a potentiometer and a generic capacitor initially to figure out the resistance needed. Just remember if you turn your potentiometer too low, it will basically be shorting out the power supply or damage the pot when the switch is pressed.
I would use any capacitor laying around along with a 10k/20k pot and fet such like CT6EP103-ND | CT6EP203-ND | TSM170N06CHC5G-ND
